An electrolytic capacitor that utilizes a metal having valve action such as aluminum is widely commonly used, since compact yet large capacitance can be obtained by shaping a valve action metal as the anodic electrode into an etching foil, etc so as to increase the surface area of the dielectric. In particular, since a solid electrolytic capacitor that employs a solid electrolyte as the electrolyte is equipped with features such as being easily made into a chip and suitable for surface mounting in addition to being compact, large capacitance, and low equivalent series resistance, it is essential for downsizing and greater functionality of electronic equipments.
A conductive polymer having high electric conductivity and superior in adherence with the oxide film layer an anodic electrode is employed as the solid electrolyte for solid electrolytic capacitor. For example, polyaniline, polypyrrole, polythiophene, polyethylenedioxythiophene or a derivative thereof are known as this conductive polymer.
For example, it is disclosed in Patent Document 1 that the anode and cathode foils are wound via a separator to form a capacitor element, this capacitor element is impregnated with EDOT and an oxidant solution, heated, and a PEDOT polymer layer is formed between the two electrodes to form a solid electrolytic capacitor.
In this solid electrolytic capacitor of Patent Document 1, since the oxidant solution shows substantial acidity, the dielectric layer which is an oxide film is eroded, increase in equivalent series resistance occurs, and withstand voltage is reduced. Accordingly, in order to prevent the erosion of the dielectric, Patent Document 2 discloses a solid electrolytic capacitor in which the solid electrolyte is formed by forming a solid electrolyte by applying a conductive polymer dispersion solution having weakened acidity or treated with alkali on the surface of the anode foil and drying, and then polymerizing a polymerizable monomer on the surface of this solid electrolyte layer.    Patent Document 1: JP 9-293639 A    Patent Document 2: JP 2007-184317 A
However, since the process will be complex in a solid electrolytic capacitor such as that in Patent Document 2, it is therefore desired to enhance the withstand voltage in a solid electrolytic capacitor formed from a solid electrolyte by applying an alkali treated conductive polymer dispersion solution and drying.
Accordingly, the present invention is proposed to solve the problems of the conventional technology as stated above, the object of which is to provide a solid electrolytic capacitor having high withstand voltage in which the solid electrolyte layer is formed with a conductive polymer dispersion solution.